The present invention relates generally to the design and construction of a lightweight high temperature turbine blade attachment structure for use in a gas turbine engine. More particularly, the present invention has one form wherein a high strength blade attachment lug, which is cast of a single crystal alloy material, is bonded to a conventional powder metal nickel alloy wheel. The high performance blade attachment lug of the present invention has higher strength properties at elevated temperatures relative to conventional nickel alloy rims with no effective increase in weight. Although the invention was developed for use in gas turbine engines, certain applications may be outside of this field.
A gas turbine engine is typical of the type of turbomachinery in which the invention described herein may be advantageously employed. It is well known that modern designers of gas turbine engines have generally utilized an axial flow compressor for compressing air to the proper pressure required for supporting the combustion of fuel in a combustion chamber. The high temperature exhaust gas exiting the combustion chamber provides the working fluid for the turbine, which powers the axial flow compressor. A power turbine that is driven by the flow of high temperature gas is utilized to turn a propeller, fan or other device. Further, the high temperature gas may be used directly as a thrust for providing motive power, such as in a turbine jet engine.
It is well known that the performance of gas turbine engines increase with the increase in the operating temperature of the flow of high temperature gas from the combustion chamber. A factor limiting the allowable temperature of the gaseous working flow from the combustion chamber is the capability of the various engine components to not degrade when exposed to the high temperature gas flow. Further, maintainability of the gas turbine engine necessitates that the various components that are subjected to the high temperature gas flow must be readily serviceable in order to minimize the down time of the gas turbine engine and the cost associated with repairs thereto. Various techniques have been utilized by engine designers to increase the allowable temperature of the gaseous working fluid, and to enhance the serviceability of engine components.
Gas turbine engine designers have generally sought to increase specific thrust, and reduce the specific fuel consumption in a gas turbine engine. However, associated with these parameters has generally been an increase in turbine inlet temperature and compressor discharge temperature. While the elevated fluid temperatures have increased the performance of the gas turbine engines it has resulted in higher blade platform, stalk, and attachment temperatures which have been generally lowered by using additional compressor discharge cooling air. Further, the prior designers of gas turbine engines have sought to reduce the attachment temperature by increasing the stalk length of the blade to isolate the wheel rim from the hot gaseous fluid flow path.
Cooling of the various components of the gas turbine engine is preferably accomplished with a minimum amount of cooling fluid, since the cooling fluid is working fluid which has been extracted from the compressor and its loss from the gas flow rapidly reduces engine efficiency. Thererfore, the use of additional cooling fluid to cool the engine components increases the specific fuel consumption. Further, the design efforts to increase the temperature of the compressor discharge fluid, which is used to cool the blade platform, stalk and attachment compounds the cooling and specific fuel consumption issues.
With reference to FIG. 1, there is illustrated a conventional gas turbine blade `a` that is carried by a turbine wheel (not illustrated). Gas turbine blade `a` has as principle regions an airfoil `b`, an attachment portion `c` and a stalk `d` which extends between the attachment portion `c` and the airfoil `a`. A blade platform `e` is disposed above the stalk `d` and is designed to shield the turbine wheel from the flow of high temperature gas from the combustion chamber. In many designs the stalk `d` function to elevate the platform `e` from the wheel in order to minimize heat transfer to the wheel, and the corresponding degradation thereof. One limitation generally associated with the prior design is that the platform `e` and the stalk `d` increase the weight, centrifugal pull and attachment stress on the rotor system.
Heretofore, there has been a need for a lightweight high temperature turbine rotor blade attachment structure for use in a gas turbine engine. A means for satisfying this need has theretofore escaped those skilled in the art.